In the past ten years, advances in biotechnology have made it possible to produce a variety of proteins for pharmaceutical applications using recombinant DNA techniques. Because proteins are larger and more complex than traditional organic and inorganic drugs (i.e. possessing multiple functional groups in addition to complex three-dimensional structures), the formulation of such proteins poses special problems. For a protein to remain biologically active, a formulation must preserve intact the conformational integrity of at least a core sequence of the protein's amino acids while at the same time protecting the protein's multple functional groups from degradation. Degradation pathways for proteins can involve chemical instability (i.e. any process which involves modification of the protein by bond formation or cleavage resulting in a new chemical entity) or physical instability (i.e. changes in the higher order structure of the protein). Chemical instability can result from deamidation, racemization, hydrolysis, oxidation, beta elimination or disulfide exchange. Physical instability can result from denaturation, aggregation, precipitation or adsorption, for example. The three most common protein degradation pathways are protein aggregation, deamidation and oxidation. Cleland et al Critical Reviews in Therapeutic Drug Carrier Systems 10(4): 307-377 (1993).
Included in the proteins used for pharmaceutical applications are antibodies. An example of an antibody useful for therapy is an antibody which binds to the CD18 antigen. CD18 is the common .beta. subunit of three heterodimeric membrane integrins restricted to leukocytes that mediate trafficking and adhesion to the vascular endothelium, particularly at sites of inflammation (for reviews see Hynes, R. O. Cell, 69:11-25 (1992); Stoolman, Cell, 56:907-910 (1989); Jutila et al. Transplantation 48(5): 727-731 (1989); Springer, T. A., Nature 346:425-434 (1990); and Albelda and Buck, FASEB J. 4:2868-2880 (1990)). The heterodimer containing CD18 and CD11b (also called MAC-1) is found primarily on neutrophils, monocytes, and some lymphocytes whose normal interaction with ICAM-1 on vascular endothelium mediates adhesion and "rolling" of cells along the vasculature. In severe hemorrhagic trauma with concurrent decrease in cardiac output and ischemia, early (within 30 min) neutrophil activation (in response to released cytokines) and up-regulation of MAC-1 increases neutrophil "stickiness". This precedes extravasation and release of proteases and superoxides that ultimately lead to further tissue damage and increased vascular permeability (Hernandez et al, Am. J. Physiol., 253(3 Pt 2): H699-H703 (1987)). Reperfusion following resuscitation exacerbates the edema and necrosis, and leads to multi-organ failure and death. Early treatment with monoclonal antibodies to CD18 in a partally-severed, ischemic rabbit ear trauma model alleviated tissue necrosis following reattachment (Vedder et al., J. Clin. Invest. 81:939-944 (1988)). A humanized antibody showed efficacy in reducing multi-organ damage and death in a rhesus monkey model of decreased cardiac output (created by depletion of 2/3 of blood volume for .about.2 hours (Mileski etal., Surgery, 108(2):206-212 (1990)). These studies point to the therapeutic potential of anti-CD18 antibodies for acute treatment of hemorrhagic shock.
Another antigen of interest for targeting with antibodies is the CD20 antigen, also known as "Bp35". CD20 is a human B cell marker which is expressed during early pre-B cell development and remains until plasma cell differentiation. The CD20 molecule may regulate a step in the activation process which is required for cell cycle initiation and differentiation and is usually expressed at very high levels on neoplastic B cells. Thus, the CD20 surface antigen can be targeted for treating B cell lymphomas. U.S. Pat. No. 5,736,137 issued Apr. 7, 1998 describes the chimeric antibody "C2B8" which binds the CD20 antigen and its use to treat B cell lymphoma.
There is a need in the art for a stable aqueous pharmaceutical formulation comprising an antibody, such as an anti-CD18 or anti-CD20 antibody, which is suitable for therapeutic use.